The syndrome of post-traumatic stress disorder (PTSD) can occur in individuals from all walks of life who are exposed to highly stressful, life-threatening events. One of the main symptoms of this disorder can be an alteration in cognitive functions; this typically includes distressing, intrusive recollections of the trauma, attempts at cognitive avoidance of these thoughts, psychogenic amnesia, restricted range of affect, concentration impairment, and hyperalertness. Although the etiology of these symptoms is not well understood, the symptoms cause considerable difficulty in many aspects of daily life. While there is no single model to explain the development of cognitive dysfunction in PTSD, important information may be gained from existing models of learning and information processing in individuals suffering from a) depression or b) anxiety and fear. These models postulate that mechanisms of hyperresponsivity to mood-congruent material and highly selective attention for threat may operate in these disorders, directly affecting other abilities which normally modulate affective and behavioral responses. Since a large percentage of individuals with PTSD suffer from depression, one avenue of exploration is to consider whether similar mechanisms are operational in PTSD. This study examines whether there are specific alterations in information processing in combat related PTSD compared to the performance of well- adjusted combat controls and psychiatric patients diagnosed exclusively with major depressive disorder (MDD). The functions under study include verbal learning, sustained attention, and perception of facial affect. Prior research indicates that the depressed (MDD) group will show a particular impairment in the three areas specified. Based on pilot data, the PTSD patients are expected to demonstrate different patterns of learning, attention, and perception which reflect the impact of combat on life experiences. This study will specifically contribute to knowledge about changes in cognitive profiles in disorders involving trauma and will help elucidate models of information processing for both traumatized and depressed populations. The study of these models has already led to major innovations in the cognitive treatment of depression. Data about information processing in patients with and without discrete trauma can further advance the treatment of anxiety and depression and significantly contribute to the very limited knowledge about effective modes of treating individuals who also suffer traumatizing events.